Cameron's 'Tantric' speech is over but the wrangling has just begun

It was a long time in the making - even David Cameron himself recently referred to it as the "Tantric approach" to speech writing.

But the big EU speech has been made, and it is now clear what the Prime Minister will offer: A referendum on the UK's membership of the EU after our relationship with Europe has been negotiated. The most likely date will be 2017.

On the whole, his previously fractious backbenchers have been calmed. I am told the response in the team room of the Commons was "very positive". If nothing else this appears to have satisfied the many critics of Europe in Mr Cameron's own party.

UKIP, meanwhile, sees this as a huge victory for them. Leader Nigel Farage told me this morning that the whole issue of UK exit from the EU would not be on the political agenda if it were not for his party.

The Deputy Prime Minister and Labour questioned the economic impact. Will the uncertainty created by our potential exit deter investors? If you ran an Asian business looking to invest millions of pounds in Europe, would you now think twice about investing that money in the UK and opt for France or Germany instead?

The reaction, therefore, from business leaders will be crucial.

But the referendum depends on some significant developments. Firstly, will the Conservatives win a majority in 2015, and will a referendum be a deal-breaker in Coalition talks if there is another inconclusive result?

Secondly, what happens if David Cameron cannot persuade his European partners to let the UK renegotiate the terms of its membership of the EU?

Will Mr Cameron then campaign for a 'No' vote? And on that the Prime Minister's response was less clear. He spoke of being an "optimist" and said that treaty changes will be necessary between now and 2017. But he has not answered the question: What if our releationship with the EU remains largely unchanged?